There is an increasing demand for computers and other electronic devices that have greater computing power and consume less energy. To meet this demand, advances are constantly being made in computer and other electronics technologies. These advances include the developments, not only in the design of the electronic devices themselves, but also in the processes that are used to manufacture these devices. One such advance in the area of manufacturing processes is referred to as immersion lithography.
Lithography systems are widely used to project an image pattern onto and thereby expose photoresist materials that have been deposited on semiconductor wafers. The photoresist material is exposed in order to create a patterned mask which may then be used to etch a complementary pattern on the surface of the wafer, or to allow dopants to be selectively deposited in the semiconductor material. The lithographic exposure may be repeated many times using various patterns during a particular manufacturing process in order to form the desired electronic components (e.g., transistors, resistors, traces, etc.).
A relatively recent improvement in the area of semiconductor manufacturing is the development of immersion lithography. In immersion lithography, a fluid such as water is placed between the last lens of the lithography system and the surface of the semiconductor wafer. Because the refractive index of the fluid is higher than the refractive index of air (which conventionally fills the space between the last lens and the wafer,) the numerical aperture of the lithography system can be increased. As a result, the lithography system can be used either to print smaller features, or to improve process latitude in comparison to conventional systems.
Immersion lithography is viewed in the in semiconductor manufacturing industry as an enabling technology. In other words, this technology enables other improvements to be made in semiconductor and electronic technologies that would not otherwise be possible. The improvement in the manufacturing process resulting from immersion lithography has delayed and/or eliminated the need to introduce some technologies (e.g., 157 nm lithography) and has at least delayed the need to introduce others (e.g., EUV lithography.) Immersion lithography has shown itself to provide significant benefits to the semiconductor industry, and virtually all leading-edge semiconductor manufacturers are implementing immersion lithography.
While immersion lithography can provide significant advantages to semiconductor manufacturers, it is necessary to closely control a number of factors relating to the use of this technology. For example, conventional immersion lithography systems include means to condition the water that is placed between the lens and the semiconductor wafer. This conditioning may include degassing the water, removing particles, and controlling the temperature of the water, among other things. One of the most critical aspects of the water conditioning is the control of its temperature, as this affects the refractive index of the water, which in turn affects the focus of the lithography system.
Because the water in the gap between the lens and the wafer may be heated from exposures by the light generated in the lithography system, it is necessary to have the water flow through the gap. The flow of water through this gap is typically managed by a flow controller. Conventional flow controllers, however, may have a number of problems that can degrade the images produced by the lithography system. These problems may, for example, include temperature variations in the water which are introduced by heating in the electronics of the flow controllers. These temperature variations can alter the refractive index of the water, as well as causing inaccuracies in the measured flow rate of the water. Another problem is that vibrations created by the flow controllers also cause variations in the refractive index of the water, resulting in degraded imaging by the system. These vibrations are typically generated by movement of parts within the flow control valves. Vibrations may also be generated by operation of a vacuum pump which removes water from the gap between the lens and the wafer. Pulsations in the vacuum generated by the vacuum pump may also cause variations in the flow rate of the water through the retention hood. Still further, if the vacuum pump removes the water from the retention hood too slowly, the water may leak out of the hood, and if the pump removes the water from the retention hood too quickly, bubbles may be introduced into the water in the retention hood.
It would therefore be desirable to provide systems and methods for controlling the flow of water or other fluids through the gap between the last lens and the semiconductor wafer in an immersion lithography system in order to reduce the problems associated with prior art systems that can degrade the effectiveness of the system.